The aim of the proposed research is to study the nature, distribution and intracellular origin of cell surface glycoproteins. First, the functionally and topographically distinct domains of the rat liver parenchymal cell surface will be isolated and purified. A new approach will be used to isolate the blood sinusoidal plasma membrane, which comprises over 50 percent of the total cell's surface area but has proven difficult to isolate using standard subcellular fractionation techniques. The approach is to use a ligand, asialofetuin, which binds specifically to membrane receptor present in this domain of the cell. The proteins and lipids of the three plasma membrane fractions will be analyzed and compared to establish whether there is extensive or minimal overlap in the molecular composition of the three regions. Focus will be primarily on proteins which will be characterized as to number, size, net charge and carbohydrate content by sodium dodecyl sulfate polyacrylamide gel electrophoresis, isoelectricfocusing and lectin labeling in gels, both alone and in combinations. In addition, the sialic-acid containing components present in the three plasma membrane domains will be identified using a radiochemical labeling technique specific for sialic-acid residues. Finally, a limited number of glycoproteins from each domain will be selected (based on abundance, unambiguous assignment as an integral membrane component, and possible presence in intracellular compartments) and kinetic experiments will be conducted in order to trace the intracellular biogenetic pathway of the cell surface glycoproteins. Labeled amino acids and specific monosaccharides will be injected into intact animals and perfused liver in a "pulse-chase" fashion followed by subcellular fractionation at various times and analysis of the rates at which the compartments (and selected components of them) are labeled.